A system, method and device for (semi-)automated e-commerce on the Internet, the WWW and other networks. Trading parties present intentions, made of more elementary components, which are used to express their willingness to engage in deals subject to constraints. Parts of intentions may be variable components. Some variable components may be associated with computational devices that transform them, optionally communicating via messages, into more specified components. This mechanism encodes business rules. By fitting intentions, contracts are formed. While fitting intentions, negotiations are carried out via the exchange of messages. Negotiations are automated by encoding users wishes as mathematical programs. Following the deal formation an optional deal improvement phase, in one-to-one mode or one-to-many mode, is carried out to improve the deal. The improvement phase may be based on a trading mechanselected from an available collection of such mechanisms including such mechanisms as constructed by users of the system.